Unraveling Vitamin B-12-Responsive Gene Regulation in Algae

作者：Helliwell Katherine E; Scaife Mark A; Sasso Severin; Araujo Ana Paula Ulian; Purton Saul; Smith Alison G^*

来源：Plant Physiology, 2014, 165(1): 388-397.

DOI：10.1104/pp.113.234369

Photosynthetic microalgae play a vital role in primary productivity and biogeochemical cycling in both marine and freshwater systems across the globe. However, the growth of these cosmopolitan organisms depends on the bioavailability of nutrients such as vitamins. Approximately one-half of all microalgal species requires vitamin B-12 as a growth supplement. The major determinant of algal B-12 requirements is defined by the isoform of methionine synthase possessed by an alga, such that the presence of the B-12-independent methionine synthase (METE) enables growth without this vitamin. Moreover, the widespread but phylogenetically unrelated distribution of B-12 auxotrophy across the algal lineages suggests that the METE gene has been lost multiple times in evolution. Given that METE expression is repressed by the presence of B-12, prolonged repression by a reliable source of the vitamin could lead to the accumulation of mutations and eventually gene loss. Here, we probe METE gene regulation by B-12 and methionine/folate cycle metabolites in both marine and freshwater microalgal species. In addition, we identify a B-12-responsive element of Chlamydomonas reinhardtii METE using a reporter gene approach. We show that complete repression of the reporter occurs via a region spanning 2574 to 290 bp upstream of the METE start codon. A proteomics study reveals that two other genes (S-Adenosylhomocysteine hydrolase and Serine hydroxymethyltransferase2) involved in the methionine-folate cycle are also repressed by B-12 in C. reinhardtii. The strong repressible nature and high sensitivity of the B-12-responsive element has promising biotechnological applications as a cost-effective regulatory gene expression tool.

• 出版日期2014-5